Amino‐Functionalized Niobium‐Carbide MXene Serving as Electron Transport Layer and Perovskite Additive for the Preparation of High‐Performance and Stable Methylammonium‐Free Perovskite Solar Cells

Abstract Perovskite solar cells have shown great potential in commercial applications due to their high performance and easy fabrication. However, the electron transport layer (ETL) materials with good optoelectrical properties and energy levels matching that of the perovskite layer still need to be explored to meet the need of commercialization. In this work, 2D Nb 2 CT x MXene nanosheets are prepared and their work function (WF) is reduced from 4.65 to 4.32 eV to match the conduction band minimum of perovskite layer by replacing the surface ‐F groups with NH 2 groups through hydrazine (N 2 H 4 ) treatment. Besides, the N 2 H 4 treated (T‐Nb 2 CT x ) MXene nanosheets with abundant NH 2 groups are incorporated into the perovskite precursor to retard the crystallization rate by forming hydrogen bond with iodine ions, which promotes the formation of high‐quality and oriented growth perovskite films. Consequently, the PVSCs with T‐Nb 2 CT x MXene ETLs and T‐Nb 2 CT x MXene nanosheets additive exhibit the highest power conversion efficiency (PCE) of 21.79% and the corresponding flexible and large‐area devices achieve the highest PCE of 19.15% and 18.31%. Meanwhile, the unencapsulated devices maintain 93% of the original PCEs after 1500 h of storage. This work demonstrates the considerable application prospects of 2D Nb 2 CT x MXene in photoelectric devices.